The present invention relates to a projection screen and a projection system and method and, more particularly, to a front projection screen and a projection method which controls the reflection of light in the horizontal and vertical directions to minimize the effects of ambient light so as to provide a high contrast image.
Projection screens are often used for audio-visual presentations at trade shows and other exhibitions. Viewers at exhibit booths are likely to stand in an arc around the front of the exhibit at some distance from a front projection screen on which images are projected. An effective presentation requires a reflected image of high intensity and good contrast. In many exhibition venues light from overhead lighting impinges on the projection screen, reducing the contrast or xe2x80x9cwashing outxe2x80x9d the projected images. Directing the light of the reflected image in a relatively narrow vertical band increases the intensity in the region of the viewers"" eyes. On the other hand, the arrangement of viewers requires that light be reflected over a substantial horizontal angle.
Generally, front projection screens are either reflective, light scattering, or refractive. The surface of light scattering screens scatters the incident light in all directions rather than reflecting it at a discrete angle. Light scattering projection screens provide a wide viewing angle both horizontally and vertically but the gain of the screen is low and images are visible only under dim lighting conditions. Refractive screens are coated with tiny glass balls and light projected at an angle to the screen is returned along the path of incidence. Refractive screens are particularly useful when the projector is positioned low relative to the screen because the light is returned along the path of incidence toward a seated audience. However, glass beaded screens can be delicate and can exhibit a granular appearance because the glass beads are of sufficient size to cause disturbing refraction involving individual picture elements. Further, the luminance provided by a refractive screen decreases substantially from the center to the edges both horizontally and vertically and the homogenous nature of the glass beads does not allow a focusing difference in the horizontal and vertical planes.
Reflective screens have surfaces exhibiting behavior governed primarily by the law of reflection; that is, the angle of incidence of light equals the angle of reflection. This type of screen provides greater gain than is available with light scattering screens and, therefore, better visibility in areas of more intense ambient light. However, the viewing angle of a planar reflective screen is narrower than that of a diffusing screen so the viewer can clearly see images only within a limited arc in front of the screen. Reflective screens commonly have a surface combining reflection and limited diffusion. Light is reflected from this type of surface in a solid angle along the nominal angle of reflection.
The physical arrangement of the projector and screen can be problematic when using front projection in an exhibit. Front projectors are seldom placed normal to the screen because the projector would obstruct the field of view of the audience. A front projector is typically located above the heads of the audience and a reflective screen is used to redirect the light to the eyes of the viewers. However, mounting the projector overhead is often not practical in a trade show or exhibit booth. Positioning the projector low relative to the screen reduces obstruction to viewing the screen, but a screen that reflects the image upward to the eyes of the audience is particularly vulnerable to glare and wash out from overhead lighting.
A front projection screen comprising multiple reflective screen elements arranged in vertical columns is disclosed in Malifaud et al., U.S. Pat. No. 5,696,625. The screen elements have either a toroidal or a cylindrical reflective surface. The curvatures of the reflective surfaces of the individual screen elements can be varied to directionally focus an image. However, focusing the reflected light by altering the curvature of individual screen elements results in a complex screen assembly. Further, the screen is adapted for use in a darkened theater setting with a projector mounted above the screen.
What is desired, therefore, is a front projection screen that provides for directional focusing of an image, protection from glare and wash out by overhead lighting, and permits the projector to be positioned near the bottom of the screen out of the line of sight of viewers.
The present invention overcomes the aforementioned drawbacks of the prior art by providing a projection screen for reflecting an image from a projector to a viewer comprising a screen defining a horizontal direction and a vertical direction and having a top and a bottom.
In a first aspect of the invention, a projection screen comprises a plurality of reflective elements. Each of the elements has an upper surface, and each element has a vertically inclined surface. The upper surface of each element is either coated with a light absorbing material, or is textured to diffuse light. The upper surface thus interferes with reflection of ambient light from the upper surface toward an adjacent vertically inclined surface of an adjacent reflective element.
In a second aspect of the invention, a projection screen is provided that reflects light from a light source in the vertical direction like a planar surface, but reflects light in the horizontal direction back toward the light source. In one embodiment, the screen is comprised of a plurality of vertically oriented light-transmissive rods. The rear surface of the rods is coated with a reflective material. In another embodiment of the invention, the screen is comprised of a plurality of pairs of reflective surfaces, each respective pair forming a generally v-shaped channel.
Each of the screen embodiments directs the ambient light away from the viewer, thereby improving image contrast. The screens of the present invention thus provide high contrast viewing even in bright ambient lighting conditions.
In a third aspect of the invention, a projection system is provided that projects a three-dimensional image.
The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.